beckers



A. E. BECKERS CATHODE RAY TUBE Feb. 7, 1956 2 Sheets-Sheet 1 Filed Jan. 26, 1953 Fig.3

Fig.2

ATTORNEYS Feb. 7, 1956 A. E. BECKERS 2,734,147

CATHODE RAY TUBE Filed Jan. 26, 1953 2 Sheets-Sheet 2 Fig. 7' 22 F' .8 Fig. 9

ALBERT E. BECKERS PWF W A TTORN EY$ Fig. /0

United States atent CATHODE RAY TUBE Albert E. Beckers, West Paterson, N. J., assignor to Allen B. Du Mont Laboratories, Inc., Clifton, N. 3., a can poration of Delaware Application January 26, 1953, Serial No. 333,026

16 Claims. (Cl. 315-23) The present invention relates to cathode ray tubes and particularly to cathode ray tubes employing electron guns which are aligned generally along the central axis of the tube but offset therefrom.

In single or multiple gun cathode ray tubes employing post deflection acceleration means and in which the electron guns are offset with respect to the central axis of the tube, the electron beam is subjected to distorting forces after leaving the deflection system and while passing through the post deflection acceleration field. Such distorting forces so effect the electron beam as to cause an unsymmetrical pair of ordinates in a cathode ray tube as, for example, an oscillograph tube. Such a condition in undesirable where the traces of the electron beam are visually observed to determine measurement conditions.

Accordingly, it is an object of the present invention to provide a cathode ray tube with means for overcoming such a condition and having symmetrical traces for visual inspection.

In accordance with my invention, I provide one or more skew correcting electrodes in the deflection system of cathode ray tubes in which the electron guns are offset from the central axis of the tube.

For a better understanding of my invention, reference may be had to the drawings in which Figure 1 is an enlarged fragmentary perspective view of a cathode ray tube embodying my invention; Figure 2 is a perspective view illustrating the deflection system of the tube of Figure 1 with one modification of the compensating electrodes of my invention; Figures 3 and 4 illustrate further modifications of the device illustrated in Figure 2; Figure 5 illustrates the trace of a cathode ray tube embodying my in vention; Figures 6 and 7 illustrate the skewed traces of a cathode ray tube in which the electron guns are offset from the central axis of the tube; Figures 8 and 9 illustrate a further modification of my invention and Figure 10 illustrates still a further modification.

Referring now to the drawing and particuflarly to Figure 1 thereof, there is illustrated a multiple gun cathode ray tube comprising a glass envelope 2 having a post defl'ection acceleration conductive ring 4 encircling the inner wall of the tube with a connector 6 adapted to connect the ring with a source of voltage. Supported within the tube is a multiple electron gun assembly 8. The assembly includes a plurality of electron guns 10 adapted to provide a beam of electrons for impingement upon a fluorescent coating, or target, 12 on the face of the tube. A

.second conductive ring electrode 5, which encircles the inner wall of the tube in the region between the guns 10 :and the accelerating ring electrode 4, is electrically connected to the assembly 8 by one or more spring contacts 7. Electrodes 5 and 4 form an electron lens, as indicated by the dashed equipotential lines 9 and 11, which,

in the normal case when electrode 4 is positive with re- ,spect to electrode 5, exerts a radially inward force on the electron beams passing therethrough. The term radially is intended to apply not only to cylindrical tubes but also to rectangular tubes and tubes of any cross-' sectional shape. Positioned between the post deflection accelerating ring 4 and the electron guns 10 are a plurality of deflection systems 14. In this connection, it will be seen that each of the deflection systems is aligned with one of the electron guns and that each of the electron guns and cooperating deflection systems are aligned generally along the central axis of the tube but ofiset therefrom. A shield 15, shown broken away for greater clarity, normally separates each of the deflection systems 14 from the other two.

With such an alignment, the normal movement of the electron beam through the field caused by the accelerating ring 4 is affected by uneven field forces which causes a skewing of the beam. Where such a beam is projected along the axis of the tube, the beam passes through a symmetrical field caused by electrodes 4 and 5 and will define a trace in which the vertical and horizontal components are substantially perpendicular as illustrated in Figure 5. Where, however, the electron beam is projected from guns located as in Figure 1, the beam is subjected to uneven field forces caused by ring 4 and will produce a trace pattern of vertical and horizontal components which are not perpendicular to each other such as illustrated in Figure 6, in which the dashed lines indicate the desired coordinates and the solid lines 17 and 19 show the traces actually achieved.

To compensate for the uneven field forces caused by the electron lens between electrodes 4 and 5, I employ a deflection system 14 including compensating deflection electrodes. Referring to Figure 2, there is illustrated, in more detail, the deflection system 14 of my invention. The deflection system 14 of Figure 2 includes deflection plates 16 and 18 which are spaced on each side of the path of the electron beam for deflecting the beam along a substantially horizontal or vertical coordinate, depending upon the position of the deflection plates with respect to the electron gun. Spaced from plates 16 and 18 are deflection plates 20 and 22 which are aligned approximately perpendicularly with respect to plates 16 and 18 and on either side of the path of the electron beam. These latter mentioned plates provide for deflection of the electron beam along a path which preferably is perpendicular to the path of that caused by plates 16 and 18. However, as heretofore described, the efliect of the field caused by ring 4 and the off axis position of the gun 10a and deflection systems 14:: causes a skewing of the trace pattern to produce a trace such as that shown in Figure 6. To compensate for that condition, intermediate defiection electrodes 24 and 26 are employed. In this connection, the electrodes 24 and 26 are connected respectively to electrodes 22 and 20 by a rigid supporting connection adapting the electrodes to be aligned substantially in the planes of deflection plates 16 and 18 respectively, and perpendicular to plates 20 and 22.

if the cathode ray tube had only a single electron gun 1dr: mounted off the axis, perpendicularity between traces 17 and 19 could be achieved in the manner just described. 'I hen the tube as a whole could be rotated to make trace 17 vertical and the now-perpendicular trace 19 horizontal. However, tubes making use of the invention almost invariably have more than one electron gun, thereby making it necessary to establish a system of coordinates, such as that indicated by the dashed lines, and adjust the deflection system 14:: so that the traces 17 and 19 are not only mutually perpendicular, but are aligned along the chosen coordinates. Other deflection systems for other electron guns (not shown in this figure) will then also be adjusted to align along the same coordinates.

in order to determine the arrangement of elements necessary to correct the scanning of a multi-gun tube, reference will be made to Figure 6, which shows a simplified deflection structure for one of the off axis guns 10a.

'tlie'r'eforq'be applied by electrodes 24 and 2-5. 'ti'on,"the'-defle'ctingfierce must vary in a predetermined "relationship to the force'of plates Ziland 22. if the relationship is linear, electrodes 24 and 26 may be connected beanrisn'ot affected bythe compensating field.

'iridic'atediri Figureobythe ar'ro'ws. In order to bring the itra'cellQii'titoparallelism with the vertical a'xis,it'is necess'ary to' s nny a deflecting force 'to'theelectrons and to make theap'plied force'perpenclicul'ar to the deflecting force of electrodes'ifiand 22. The correcting force may,

in addidirectly 'toplates' 22ahd "28 respectively, as shown in Figure ofby fthe'short'connecting'links 2S and 27. if some 'otlier'rela'tionshipis desired,'theelectrodes 2d and 26 may befreplaced'by hriguI'arlydi-s'posed' electrodes 2% and 3t), 'ss"shownin Figure 3, or by curved electrodes, as shown in Figure o i "In order to' correct for the a'ngulardisplacemcnt of trace 17 with respect to the horizontal axis, plates 16 and 18"are rotated'toian opposite angular rotation as shown. It will be understood that the particular'connections previously described for the compensating electrodes 24 and lfi'ofoneof the g'unsin the' tube would be reversed in its side by'side relationship with a neighboring gun in the tube. The'efiect of the deflection'electrodes of a gun such as gun b in Figure l isto produce a trace such as that shown by the solid lines 17 and I? in Figure 7 when the With fields applied by the respective compensating electrodes to "deflection structures 14a and 1450f Figure l, the resulting tracelis'that of Figure 5.

Another'anodification of my invention, which I have foundbseful in compensating for uneven post accelerat- "i'ngfforces caused by the ficld between electrodes 4 and 5, 'isshown in Figures 8, 9, and 10 in Figure 8, an electron gun assembly similar to those illustrated in Figure l includes the electron gun 1i and a deflection system including plates l6, 18, ','a'nd 22 as in Figure 2. in this modifi'cat'ion, however, the compensating electrodes 36 and 33 are oblong metal strips such as shown in Figure 9. These strips arealigned with deflection 'plates 16 and 18 as shown and 'are rigidly supported by connecting wires 4!) and 42, 'which connect respectively with plates 22 and 20, not

shown. Deflection electrodes 36 and 38 function in substantially the same manner as the compensating deflectionelectrodes heretoforedescribed, except that they afiect 'theielc'ctron beam after it has passed both pairs of deflecnon plates.

Figure "10 illustrates'another compensating electrode 44 similar to'tliat shown in Figure 9, except that its width varies fronrone'end to the other to compensate for non- -linear bending. Compensating electrode 44 is connected in the deflection system in the same manner as deflection electrodes 36 and 38desc'ribed in connection with Figure 8.

The compensating electrodes 24 and 26, or their equivalents,ha've been shown connected to the plates 20 and 22 to receive deflecting signals therefrom. As an alternative, compensating electrodes 24 and'26 could be insulated from plates 20'and22, as, for instance, by linear or non-linear increase or reduction in amplitude.

Furthermore, the compensating electrodes 24 and 26 may be'bias'ed to a difi'erent center voltage than the other "electrodesin gun 10"or deflection structure 14 (Figure l) in order tocompens'ate, in a known manner, for astigmaofthe electron beam spot on target 12.

"In order'to'simplify the deflecting structure 14, "one of the eenr ensanng lebtrodes 24 or 26'might be either elimi- Qil) a d nated or connected to a fined-potential electrodefsuch' as electrode 5, and a sc-called single-ended compensating deflection of the electron beam would take place.

Still further modifications may be utilized within the scope of the invention as determined by the following claims.

What i claim is:

1. In a cathode ray tube having a fluorescent coating and an electron gun for directing a beam of electrons onto said coating; an electrostatic deflection system disposed between. as 'LI'tl and said coating; said system comprising: a first pair of deflection plates located between said gun and said coating and spaced apart on diametrically opposite sides of said beam; :1 second pair of deflection plates iocatcd between said pair of first deflection plates and said coating and spaced apart on diametrically opposite sides of said beam, said second pair of plates being substantially perpendicular to said first pair of plates; and an astigmatic electron lens comprisinga pair of compcnsating electrodes co-acting with said first pair of deilection plates, said compensating electrodes being located on diametrically opposite sides of said electron beam and at an angie to said first pair of plates, one of said compensating electrodes being connected to each plate respeetiveiy of said first pair of plates.

2. in a cathode ray tube having a fluorescent coating and an electron gun for directing a beam of electrons'onto said writing; an electrostatic deflection system disposed between said gun and said coating; said'system comprising: a first pair of deflection plates'located between said'gun and said coating and spaced apart on diametrically opposite sides of said beam; a second pair of deflection plates sides of said beam, said second pair of plates being substantially perpendicular to said first pair of plates; and an astigmatic electron lens comprising a pair of compensating electrodes co-acting with said first pair of do 'tlection plates, said compensating electrodes being located in the'space between said first and said second pair of deflection plates and on diametrically opposite sides of said electron beam and at an angle to said first pair of plates,'one of said compensating electrodes being connccted to each plate respectively of said first pair of plates.

3. A cathode ray tube comprising a target; an electron gun forming a source of a beam of electrons; and a plurality of electrodes arranged along the path traversed by said beam, said electrodes comprising a first pair of deflecting'plates; a second pair of deflecting plates arranged at an angle to said first pair and located between said first pair and said target; means forming an electron lens between said gun and said target; and an astigmaticelectron lens comprising a compensating electrode'co-acting with said first pair ofdcfl'ection plates and arranged at an angle to said first pair of plates and located between said gun and said electron lens toprovide an asymmetrical skewing deflection for said beam thereby correcting for the'deflection of said beam in said electron lens.

4. The device of claim 3 in which said compensating electrode is located between said gun and said first pair of plates.

5. The device of claim 3 in which said compensating electrode is located between said first pair of plates and said second pair of plates.

6. The device of claim 3 in WhiChSflid compensating electrode is located between said second pair of plates and said electron lens.

7. The device of claim 3 in which'said compensating electrode is connected directly to one plate of 'sa'id 'first pair.

"of plates.

10. A cathode ray tube comprising a target; an electron gun forming a source of an electron beam, and a plurality of electrodes arranged along the path traversed by said beam, said electrodes comprising a first pair of deflecting plates; a second pair of deflecting plates arranged at an angle to said first pair and located between said first pair and said target; means forming an electron lens between said gun and said target; and a pair of defleeting. compensating electrodes on diametrically opposite sides of said beam arranged at an angle to said first pair of plates and located between said gun and said electron lens to correct for the deflection of said beam in such electron lens, each electrode of said pair of compensating electrodes being connected to a plate respectively of said first pair of plates.

11. The device of claim in which said compensating electrodes are substantially parallel to each other over their operating length.

12. The device of claim 10 in which said compensating electrodes are at an angle to each other.

13. The device of claim 10 in which said compensating electrodes are curved.

14. The device of claim 13 in which said compensating electrodes are curved in a direction substantially perpendicular to said electron beam.

15. A cathode ray tube comprising a target; an electron gun forming a source of an electron beam; and a plurality of electrodes arranged along the path traversed by said beam, said electrodes comprising a first pair of deflecting plates; a second pair of deflecting plates arranged at an angle to said first pair and located between said first pair and said target; means forming an electron lens between said gun and said target; a pair of compensating deflecting electrodes on diametrically opposite sides of said beam arranged at an angle to said first pair of plates and located between said gun and said electron lens to correct for the deflection of said beam in said electron lens; a source of signal voltage connected to said first pair of deflecting plates; and a second source of a similar signal voltage connected to said compensating deflecting electrode.

16. The device of claim 15 in which said second source is a portion of said first source.

References Cited in the file of this patent UNITED STATES PATENTS 

1. IN A CATHODE RAY TUBE HAVING A FLUORESCENT COATING AND AN ALECTRON GUN FOR DIRECTING A BEAM OF ELECTRONS ONTO SAID COATING; AN ELECTROSTATIC DEFLECTION SYSTEM DISPOSED BETWEEN SAID GUN AND SAID COATING; SAID SYSTEM COMPRISING A FIRST PAIR OF DEFLECTION PLATES LOCATED BETWEEN SAID GUN AND SAID COATING AND SPACED APART ON DIAMETRICALLY OPPOSITE SIDES OF SAID BEAM; A SECOND PAIR OF DEFLECTION PLATES LOCATED BETWEEN SAID PAIR OF FIRST DEFLECTION PLATES AND SAID COATING AND SPACED APART ON DIAMETRICALLY OPPOSITE SIDES OF SAID BEAM, SAID SECOND PAIR OF PLATES BEING SUBSTANTIALLY PERPENDICULAR TO SAID FIRST PAIR OF PLATES; AND AN ASTIGMATIC ELECTRON LENS COMPRISING A PAIR OF COMPENSATING ELECTRODES CO-ACTING WITH SAID FIRST PAIR OF DEFLECTION PLATES, SAID COMPENSATING ELECTRODES BEING LOCATED ON DIAMETRICALLY OPPOSITE SIDES OF SAID ELECTRON BEAM AND AT AN ANGLE TO SAID FIRST PAIR OF PLATES, ONE OF SAID COMPENSATING ELECTRODES BEING CONNECTED TO EACH PLATE RESPECTIVELY OF SAID FIRST PAIR OF PLATES. 